This invention is directed generally to improvements in color television receivers, and particularly to color demodulation and matrixing of demodulated color-difference signals.
Many conventional color television receivers employ a B-Y demodulator and an R-Y demodulator for generating B-Y and R-Y color-difference signals from the color component of a received television signal. To develop a G-Y color-difference signal, the B-Y and R-Y color-difference signal is applied to a resistor matrix. The matrix adds the B-Y and R-Y signals in weighted proportions to develop an output voltage corresponding to the G-Y color-difference signal.
One problem with the resistor matrix approach described above is that the frequency response of the G-Y color-difference signal is degraded. The typically large value resistors and their associated capacitances cause the G-Y signal to roll off at an undesirably low frequency.
Another problem associated with typical resistor matrixes is that they tend to produce G-Y signals having a D.C. component which is different from the D.C. component associated with the R-Y and B-Y signals. In addition, the D.C. component of the G-Y signal tends not to track with the D.C. components of the B-Y and R-Y signal with temperature variations.
Yet another drawback of prior demodulation systems has been their inability to develop color-difference signals having an amplitude which is as large as desired.
Because of the problems mentioned above, prior demodulation and matrixing systems have proven to be less then perfectly satisfactory. The fact tha the G-Y signal tends to have a D.C. component which is different from and which does not track with the D.C. components of the other color-difference signals makes it difficult to D.C. couple the color-difference signals to further stages of color-difference amplifiers.